Process files only supported by plugins (#15433)

changelog_unreleased/cli/15433.md

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+#### Process files only supported by plugins (#15433 by @sosukesuzuki)
+
+In Prettier 3.0, when specifying a directory from the CLI, only files with default supported extensions were processed.
+
+In the following scenario, not just `foo.js` but also `foo.astro` should be formatted:
+
+```
+# Prettier stable version
+
+$ ls .
+foo.js foo.astro
+
+$ cat .prettierrc
+{ "plugins": ["prettier-plugin-astro"] }
+
+$ prettier --write .
+foo.js 20ms
+```
+
+With this update, both `foo.js` and `foo.astro` will now be formatted:
+
+```
+# Prettier main branch
+
+$ prettier --write .
+foo.js 20ms
+foo.astro 32ms
+```
+
+You can replace `prettier "**/*" --ignore-unknown` with `prettier .` since they are equivalent now.